If `Allocator::select_on_container_copy_construction` exists and has the right signature, the allocator will be constructed from its result.
If如果 `Allocator::select_on_container_copy_construction` exists and has the right signature, the allocator will be constructed from its result.存在且具有正确的签名,则分配器将根据其结果进行构造。
If如果 `Allocator::select_on_container_copy_construction`exists and has the right signature, the allocator will be constructed from its result.存在且具有正确的签名,则分配器将根据其结果进行构造。